Open Category Manager from menu. Select category to edit. Modify field name and type(Mask/Unmask). Add more fields by clicking + icon. Click ✔ icon to save category. Empty fields will be excluded from category. Modifying Category fields will not affect existing credentials.

In Category Manager click + icon.

Swipe category right in category manager to delete it. Deleting category won't affect credentials. Credentials will move to uncategorised.